Refrigeration apparatus

ABSTRACT

In an air-conditioning apparatus, refrigerant flows sequentially through a compressor, an outdoor heat exchanger, expansion mechanisms, and an indoor heat exchanger during a cooling operation, and refrigerant flows sequentially through the compressor, the indoor heat exchanger, the expansion mechanisms, and the outdoor heat exchanger during a heating operation. Capacity of the outdoor heat exchanger is 30% to 90% of the indoor heat exchanger. The expansion mechanisms include an upstream-side and downstream-side expansion mechanisms depressurizing refrigerant from high to intermediate pressure, and from intermediate to low pressure in the refrigerant cycle, respectively. The refrigerant is R32. A refrigerant storage tank that stores the intermediate pressure refrigerant is provided between the upstream-side and downstream side expansion mechanisms. The refrigerant storage tank stores an excess refrigerant produced during the cooling operation due to capacity of the outdoor heat exchanger relative the indoor heat exchanger.

TECHNICAL FIELD

The present invention relates to a refrigeration apparatus, andparticularly relates to a refrigeration apparatus capable of performinga cooling operation and a heating operation.

BACKGROUND ART

In conventional refrigeration apparatuses such as air-conditioningapparatuses capable of air-cooling and air-warming operations, there isa difference between the optimal refrigerant quantity for an air-coolingoperation (cooling operation) and the optimal refrigerant quantity foran air-warming operation (heating operation). Accordingly, there is adifference between the capacity of an outdoor heat exchanger functioningas a heat radiator of refrigerant during the air-cooling operation andthe capacity of an indoor heat exchanger functioning as a heat radiatorof refrigerant during the air-warming operation. Because the capacity ofthe outdoor heat exchanger is greater than the capacity of the indoorheat exchanger, refrigerant that cannot be accommodated by the indoorheat exchanger during the air-warming operation is temporarily stored ina refrigerant storage tank or the like connected to an intake side of acompressor.

SUMMARY OF THE INVENTION

However, in the refrigeration apparatus described above, when ahigh-performance heat exchanger such as the one disclosed in PatentLiterature 1 (Japanese Laid-open Patent Application No. 6-143991) isused as an outdoor heat exchanger, the capacity of the outdoor heatexchanger becomes equal to or less than the capacity of the indoor heatexchanger. Therefore, in this case, refrigerant that cannot beaccommodated in the outdoor heat exchanger during the air-coolingoperation (excess refrigerant) is produced, and the quantity of thisrefrigerant exceeds the quantity that can be stored in the refrigerantstorage tank or the like.

An object of the present invention is to provide a refrigerationapparatus capable of performing a cooling operation and a heatingoperation, wherein the excess refrigerant produced during the coolingoperation can be accommodated when the capacity of the outdoor heatexchanger is equal to or less than the capacity of the indoor heatexchanger.

A refrigeration apparatus according to a first aspect is a refrigerationapparatus in which a refrigerant flows sequentially through acompressor, an outdoor heat exchanger, expansion mechanisms, and anindoor heat exchanger during a cooling operation, and the refrigerantflows sequentially through the compressor, the indoor heat exchanger,the expansion mechanisms, and the outdoor heat exchanger during aheating operation. In this refrigeration apparatus, the indoor heatexchanger is a cross-fin type heat exchanger and the outdoor heatexchanger is a stacked heat exchanger. Moreover, the expansionmechanisms include an upstream-side expansion mechanism fordepressurizing the refrigerant and a downstream-side expansion mechanismfor depressurizing the refrigerant that has been depressurized in theupstream-side expansion mechanism, and a refrigerant storage tank forstoring the refrigerant depressurized by the upstream-side expansionmechanism is provided between the upstream-side expansion mechanism andthe downstream-side expansion mechanism.

A capacity of a stacked heat exchanger is less than a capacity of across-fin type heat exchanger having similar heat exchange performance.In a case of a refrigeration apparatus in which the outdoor heatexchanger and the indoor heat exchanger are both cross-fin type heatexchangers, and then only the outdoor heat exchanger is changed to astacked heat exchanger having similar heat exchange performance, thecapacity of this stacked outdoor heat exchanger will then not only beless than the capacity of a cross-fin type outdoor heat-exchanger, butwill also be less than the capacity of the cross-fin type indoor heatexchanger connected thereto.

Therefore, in such a refrigeration apparatus, an excess refrigerant isproduced during the cooling operation due to the capacity of the outdoorheat exchanger being less than the capacity of the indoor heatexchanger. There is a risk that a refrigerant control will be hinderedwhen too much of this excess refrigerant spreads from the indoor heatexchanger having a gas-phase portion to portions as far as an intakeside of the compressor.

In view of this, the refrigerant storage tank for storing therefrigerant depressurized by the upstream-side expansion mechanism isprovided between the upstream-side expansion mechanism and thedownstream-side expansion mechanism, and the excess refrigerant thatcould not be accommodated in the outdoor heat exchanger during thecooling operation is thereby accommodated in the refrigerant storagetank positioned in the vicinity of the downstream side of the outdoorheat exchanger.

It is thereby possible to prevent hindrances to the refrigerant controlin this refrigeration apparatus, because it is possible to prevent toomuch refrigerant from spreading from the indoor heat exchanger having agas-phase portion to portions as far as the intake side of thecompressor.

A refrigeration apparatus according to a second aspect is arefrigeration apparatus in which a refrigerant flows sequentiallythrough a compressor, an outdoor heat exchanger, expansion mechanisms,and an indoor heat exchanger during a cooling operation, and refrigerantflows sequentially through the compressor, the indoor heat exchanger,the expansion mechanisms, and the outdoor heat exchanger during aheating operation. In this refrigeration apparatus, a capacity of theoutdoor heat exchanger is 100% or less of a capacity of the indoor heatexchanger. Moreover, the expansion mechanisms include an upstream-sideexpansion mechanism for depressurizing the refrigerant and adownstream-side expansion mechanism for depressurizing the refrigerantthat has been depressurized in the upstream-side expansion mechanism,and a refrigerant storage tank for storing the refrigerant depressurizedby the upstream-side expansion mechanism is provided between theupstream-side expansion mechanism and the downstream-side expansionmechanism.

When the capacity of the outdoor heat exchanger is equal to or less thanthe capacity of the indoor heat exchanger, an excess refrigerant isproduced during the cooling operation. There is a risk that arefrigerant control will be hindered when too much of this excessrefrigerant spreads from the indoor heat exchanger having a gas-phaseportion to portions as far as an intake side of the compressor.

In view of this, the refrigerant storage tank for storing therefrigerant depressurized by the upstream-side expansion mechanism isprovided between the upstream-side expansion mechanism and thedownstream-side expansion mechanism, and the excess refrigerant thatcould not be accommodated in the outdoor heat exchanger during thecooling operation is thereby accommodated in the refrigerant storagetank positioned in the vicinity of the downstream side of the outdoorheat exchanger.

It is thereby possible to prevent hindrances to the refrigerant controlin this refrigeration apparatus, because it is possible to prevent toomuch refrigerant from spreading from the indoor heat exchanger having agas-phase portion to portions as far as the intake side of thecompressor.

A refrigeration apparatus according to a third aspect is therefrigeration apparatus according to the first or second aspect, whereinthe refrigerant is R32.

When R32 is used as the refrigerant in the refrigeration apparatus, arefrigerator oil sealed with the refrigerant in order to lubricate thecompressor tends to have extremely low solubility in low-temperatureconditions. Therefore, at a low pressure in the refrigeration cycle, thesolubility of the refrigerator oil greatly decreases due to the decreasein a refrigerant temperature. When R32 is used as the refrigerant in aconventional refrigeration apparatus having the refrigerant storage tankon the intake side of the compressor, for example, the refrigerant andthe refrigerator oil separate into two layers in the refrigerant storagetank which has a low pressure in the refrigeration cycle, and therefrigerator oil has difficulty returning to the compressor.

However, because the refrigerant storage tank is provided between theupstream-side expansion mechanism and the downstream-side expansionmechanism in this refrigeration apparatus as described above, therefrigerator oil returns more readily to the compressor, in comparisonto cases in which the refrigerant storage tank is provided to the intakeside of the compressor.

Thus, in this refrigeration apparatus, due to the refrigerant storagetank being provided between the upstream-side expansion mechanism andthe downstream-side expansion mechanism, it is possible to resolve notonly the problem of the excess refrigerant produced by the capacity ofthe outdoor heat exchanger being equal to or less than the capacity ofthe indoor heat exchanger, due to factors such as a stacked heatexchanger being used as the outdoor heat exchanger, but also the problemof oil returning to the compressor, caused by using R32 as therefrigerant.

A refrigeration apparatus according to a fourth aspect is therefrigeration apparatus according to any of the first through thirdaspects, wherein the outdoor heat exchanger is a stacked heat exchangerhaving a plurality of flat tubes arrayed so as to be superposed setapart by gaps, and fins sandwiched between the adjacent flat tubes.

In this refrigeration apparatus, similar to the refrigeration apparatusaccording to the first through third aspects described above, therefrigerant quantity in the refrigeration apparatus is reduced becausethe capacity of the outdoor heat exchanger is equal to or less than thecapacity of the indoor heat exchanger. The excess refrigerant isproduced during the cooling operation in this refrigeration apparatus,but because this excess refrigerant can be accommodated in therefrigerant storage tank, hindrances to the refrigerant control can beprevented.

A refrigeration apparatus according to a fifth aspect is therefrigeration apparatus according to any of the first through thirdaspects, wherein the outdoor heat exchanger is a stacked heat exchangerhaving a plurality of flat tubes arrayed so as to be superposed setapart by gaps, and fins having notches formed therein where the flattubes are inserted.

In this refrigeration apparatus, similar to the refrigeration apparatusaccording to the first through third aspects described above, therefrigerant quantity in the refrigeration apparatus is reduced becausethe capacity of the outdoor heat exchanger is equal to or less than thecapacity of the indoor heat exchanger. The excess refrigerant isproduced during the cooling operation in this refrigeration apparatus,but because this excess refrigerant can be accommodated in therefrigerant storage tank, hindrances to the refrigerant control can beprevented.

A refrigeration apparatus according to a sixth aspect is therefrigeration apparatus according to any of the first through thirdaspects, wherein the outdoor heat exchanger is a stacked heat exchangerhaving flat tubes molded into serpentine shapes, and fins insertedbetween mutually adjacent surfaces of the flat tubes.

In this refrigeration apparatus, similar to the refrigeration apparatusaccording to the first or second aspect described above, the refrigerantquantity in the refrigeration apparatus is reduced because the capacityof the outdoor heat exchanger is equal to or less than the capacity ofthe indoor heat exchanger. The excess refrigerant is produced during thecooling operation in this refrigeration apparatus, but because thisexcess refrigerant can be accommodated in the refrigerant storage tank,hindrances to the refrigerant control can be prevented.

A refrigeration apparatus according to a seventh aspect is therefrigeration apparatus according to the second aspect, wherein therefrigerant is R32.

When R32 is used as the refrigerant in the refrigeration apparatus, arefrigerator oil sealed with the refrigerant in order to lubricate thecompressor tends to have extremely low solubility in low-temperatureconditions. Therefore, at a low pressure in the refrigeration cycle, thesolubility of the refrigerator oil greatly decreases due to the decreasein a refrigerant temperature. When R32 is used as the refrigerant in aconventional refrigeration apparatus having the refrigerant storage tankon the intake side of the compressor, for example, the refrigerant andthe refrigerator oil separate into two layers in the refrigerant storagetank which has a low pressure in the refrigeration cycle, and therefrigerator oil has difficulty returning to the compressor.

However, because the refrigerant storage tank is provided between theupstream-side expansion mechanism and the downstream-side expansionmechanism in this refrigeration apparatus as described above, therefrigerator oil returns more readily to the compressor, in comparisonto cases in which the refrigerant storage tank is provided to the intakeside of the compressor.

Thus, in this refrigeration apparatus, due to the refrigerant storagetank being provided between the upstream-side expansion mechanism andthe downstream-side expansion mechanism, it is possible to resolve notonly the problem of the excess refrigerant produced by the capacity ofthe outdoor heat exchanger being equal to or less than the capacity ofthe indoor heat exchanger, but also the problem of oil returning to thecompressor, caused by using R32 as the refrigerant.

A refrigeration apparatus according to an eighth aspect is therefrigeration apparatus according to the second or seventh aspect,wherein the outdoor heat exchanger and the indoor heat exchanger arecross-fin type heat exchangers, and a diameter of heat transfer tubes inthe outdoor heat exchanger is designed to be less than a diameter ofheat transfer tubes in the indoor heat exchanger.

In this refrigeration apparatus, similar to the refrigeration apparatusaccording to the second aspect described above, the refrigerant quantityin the refrigeration apparatus is reduced because the capacity of theoutdoor heat exchanger is equal to or less than the capacity of theindoor heat exchanger. The excess refrigerant is produced during thecooling operation in this refrigeration apparatus, but because thisexcess refrigerant can be accommodated in the refrigerant storage tank,hindrances to the refrigerant control can be prevented.

A refrigeration apparatus according to a ninth aspect is therefrigeration apparatus according to any of the first through eighthaspects, further provided with a bypass tube for leading a gas componentof the refrigerant accumulated in the refrigerant storage tank to thecompressor or to a refrigerant tube on an intake side of the compressor.

In this refrigeration apparatus, the refrigerant depressurized in theupstream-side expansion mechanism is separated into a liquid componentand the gas component in the refrigerant storage tank, and the gascomponent heads toward the bypass tube.

The gas component, which does not contribute to evaporation, therebyceases to flow into the outdoor heat exchanger functioning as anevaporator of the refrigerant during the heating operation in thisrefrigeration apparatus, it is therefore possible to proportionatelyreduce the flow rate of the refrigerant flowing through the outdoor heatexchanger functioning as an evaporator of the refrigerant, and adepressurization loss in the refrigeration cycle can be reduced.

A refrigeration apparatus according to a tenth aspect is therefrigeration apparatus according to the ninth aspect, wherein thebypass tube has a flow rate adjustment mechanism.

When the operating frequency of the compressor is high, there is a riskthat a gas-liquid two-phase refrigerant from the refrigerant storagetank will pass through the bypass tube, return to the compressor or theintake tube of the compressor, and be drawn into the compressor.

However, in this refrigeration apparatus, because the flow rateadjustment mechanism is provided to the bypass tube, the liquidcomponent of the gas-liquid two-phase refrigerant is depressurized andevaporated.

It is thereby possible in this refrigeration apparatus to prevent theliquid component from returning to the compressor or the intake tube ofthe compressor.

During the heating operation in this refrigeration apparatus, therefrigerant that has passed through the flow rate adjustment mechanismconverges with the refrigerant which has evaporated in the outdoor heatexchanger, and then heads to the compressor or the intake tube of thecompressor. At this time, in the case that the flow rate adjustmentmechanism is an electric expansion valve, the state of the refrigerantjust before being drawn into the compressor can be adjusted moreoptimally by controlling the valve opening degree. Moreover, because theflow rate of the refrigerant returning to the compressor can beincreased or reduced by controlling the valve opening degree of the flowrate adjustment mechanism, the refrigerant circulation flow rate, i.e.the flow rate of the refrigerant flowing through the indoor heatexchanger can be controlled according to the refrigeration load on theindoor heat exchanger side.

A refrigeration apparatus according to an eleventh aspect is therefrigeration apparatus according to any of the first through tenthaspects, wherein the refrigerant storage tank is a gas-liquid separator.

In this refrigeration apparatus, the refrigerant storage tank composedof the gas-liquid separator has both a function of accumulating a liquidcomponent and a function of separating the liquid component and a gascomponent.

This contributes to simplifying the apparatus configuration in thisrefrigeration apparatus because there is no need to provide both acontainer having a refrigerant storage function and a container having agas-liquid separating function.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram of an air conditioningapparatus as a refrigeration apparatus according to an embodiment of thepresent invention.

FIG. 2 is a schematic front view of an indoor heat exchanger.

FIG. 3 is an external perspective view of an outdoor heat exchanger.

FIG. 4 is a graph showing the outdoor heat exchanger capacity/indoorheat exchanger capacity ratio according to capability.

FIG 5 is a schematic cross-sectional view of a refrigerant storage tankin Modification 1.

FIG. 6 is an external perspective view of an outdoor heat exchanger inModification

FIG. 7 is a longitudinal cross-sectional view of the outdoor heatexchanger in Modification 2.

DESCRIPTION OF EMBODIMENTS

An embodiment of the refrigeration apparatus according to the presentinvention and modifications thereof are described below with referenceto the drawings. The specific configuration of the refrigerationapparatus according to the present invention is not limited to thefollowing embodiment or the modifications thereof, and can be alteredwithin a range that does not deviate from the scope of the invention.

(1) Configuration of Air-Conditioning Apparatus

FIG. 1 is a schematic configuration diagram of an air-conditioningapparatus 1 as a refrigeration apparatus according to an embodiment ofthe present invention.

The air-conditioning apparatus 1 is a refrigeration apparatus capable ofperforming an air-cooling operation as a cooling operation and anair-warming operation as a heating operation by performing avapor-compression refrigeration cycle. The air-conditioning apparatus 1is configured primarily from the connection between an outdoor unit 2and an indoor unit 4. The outdoor unit 2 and the indoor unit 4 areconnected via a liquid refrigerant communication tube 5 and a gasrefrigerant communication tube 6. Specifically, a vapor-compressionrefrigerant circuit 10 of the air-conditioning apparatus 1 is configuredfrom the connection between the outdoor unit 2 and the indoor unit 4 viathe refrigerant communication tubes 5, 6.

<Indoor Unit>

The indoor unit 4, which is installed inside a room, constitutes part ofthe refrigerant circuit 10. he indoor unit 4 primarily has an indoorheat exchanger 41.

The indoor heat exchanger 41 is a heat exchanger that functions as anevaporator of refrigerant to cool indoor air during the air-coolingoperation, and functions as a heat radiator of refrigerant during theair-warming operation to heat indoor air. A liquid side of the indoorheat exchanger 41 is connected to the liquid refrigerant communicationtube 5, and a gas side of the indoor heat exchanger 41 is connected tothe gas refrigerant communication tube 6.

The indoor heat exchanger 41, which is a cross-fin type heat exchanger,has primarily heat transfer fins 411 and heat transfer tubes 412, asshown in FIG. 2. FIG 2 is a front view of the indoor heat exchanger 41.The heat transfer fins 411 are thin aluminum flat plates, andpluralities of through-holes are formed in the heat transfer fins 411.The heat transfer tubes 412 have straight tubes 412 a inserted throughthe through-holes of the heat transfer fins 411, and U-shaped tubes 412b, 412 c linking the ends of adjacent straight tubes 412 a together. Thestraight tubes 412 a are firmly adhered to the heat transfer fins 411 byundergoing an expanding process after being inserted through thethrough-holes of the heat transfer fins 411. The straight tubes 412 aand the first U-shaped tubes 412 b are formed integrally, and the secondU-shaped tubes 412 c are linked to the ends of the straight tubes 412 aby welding, soldering, or the like, after being inserted through thethrough-holes of the heat transfer fins 411 and undergoing the expandingprocess.

The indoor unit 4 also has an indoor fan 42 for drawing indoor air intothe indoor unit 4 and supplying the air back into the room as suppliedair after the air has exchanged heat with the refrigerant in the indoorheat exchanger 41. The indoor fan 42 is a centrifugal fan, a multi-bladefan, or the like driven by an indoor fan motor 43.

The indoor unit 4 has an indoor-side control part 44 for controlling theactions of the components constituting the indoor unit 4. Theindoor-side control part 44, which has a microcomputer, a memory, andthe like for performing control on the indoor unit 4, is designed to becapable of exchanging control signals and the like with a remotecontroller (not shown), and also of exchanging control signals and thelike with the outdoor unit 2 via a transmission line 8 a.

<Outdoor Unit>

The outdoor unit 2, which is installed outside of the room, constitutespart of the refrigerant circuit 10. The outdoor unit 2 has primarily acompressor 21, a switching mechanism 22, an outdoor heat exchanger 23, afirst expansion mechanism 24, a refrigerant storage tank 25, a secondexpansion mechanism 26, a liquid-side shutoff valve 27, and a gas-sideshutoff valve 28.

The compressor 21 is a device for compressing low-pressure refrigerantin the refrigeration cycle to a high pressure. The compressor 21 has asealed structure in which a rotary, scroll, or other type ofdisplacement compression element (not shown) is rotatably driven by acompressor motor 21 a controlled by an inverter. An intake tube 31 isconnected to the intake side of the compressor 21, and a discharge tube32 is connected to the discharge side. The intake tube 31 is arefrigerant tube connecting the intake side of the compressor 21 and afirst port 22 a of the switching mechanism 22. An accumulator 29 isprovided to the intake tube 31. The discharge tube 32 is a refrigeranttube connecting the discharge side of the compressor 21 and a secondport 22 b of the switching mechanism 22.

The switching mechanism 22 is a mechanism for switching the direction ofrefrigerant flow in the refrigerant circuit 10. During the air-coolingoperation, the switching mechanism 22 performs a switch that causes theoutdoor heat exchanger 23 to function as a heat radiator of refrigerantcompressed in the compressor 21, and causes the indoor heat exchanger 41to function as an evaporator of refrigerant that has radiated heat inthe outdoor heat exchanger 23. Specifically, during the air-coolingoperation, the switching mechanism 22 performs a switch thatinterconnects the second port 22 b and a third port 22 c, andinterconnects the first port 22 a and a fourth port 22 d. The dischargeside of the compressor 21 (the discharge tube 32 herein) and the gasside of the outdoor heat exchanger 23 (a first gas refrigerant tube 33herein) are thereby connected (refer to the solid lines of the switchingmechanism 22 in FIG. 1). Moreover, the intake side of the compressor 21(the intake tube 31 herein) and the gas refrigerant communication tube 6side (a second gas refrigerant tube 34 herein) are connected (refer tothe solid lines of the switching mechanism 22 in FIG. 1). During theair-warming operation, the switching mechanism 22 performs a switch thatcauses the outdoor heat exchanger 23 to function as an evaporator ofrefrigerant that has radiated heat in the indoor heat exchanger 41, andcauses the indoor heat exchanger 41 to function as a heat radiator ofrefrigerant that has been compressed in the compressor 21. Specifically,during the air-warming operation, the switching mechanism 22 performs aswitch that interconnects the second port 22 b and the fourth port 22 d,and interconnects the first port 22 a and the third port 22 c. Thedischarge side of the compressor 21 (the discharge tube 32 herein) andthe gas refrigerant communication tube 6 side (the second gasrefrigerant tube 34 herein) are thereby connected (refer to the dashedlines of the switching mechanism 22 in FIG. 1). Moreover, the intakeside of the compressor 21 (the intake tube 31 herein) and the gas sideof the outdoor heat exchanger 23 (the first gas refrigerant tube 33herein) are connected (refer to the dashed lines of the switchingmechanism 22 in FIG. 1). The first gas refrigerant tube 33 is arefrigerant tube connecting the third port 22 c of the switchingmechanism 22 and the gas side of the outdoor heat exchanger 23. Thesecond gas refrigerant tube 34 is a refrigerant tube connecting thefourth port 22 d of the switching mechanism 22 and the gas refrigerantcommunication tube 6 side. The switching mechanism 22 herein is afour-way switching valve.

The outdoor heat exchanger 23 is a heat exchanger that functions as aheat radiator of refrigerant that uses outdoor air as a cooling sourceduring the air-cooling operation, and functions as an evaporator ofrefrigerant that uses outdoor air as a heating source during theair-warming operation. The liquid side of the outdoor heat exchanger 23is connected to a liquid refrigerant tube 35, and the gas side isconnected to the first gas refrigerant tube 33. The liquid refrigeranttube 35 is a refrigerant tube connecting the liquid side of the outdoorheat exchanger 23 and the liquid refrigerant communication tube 5 side.

The outdoor heat exchanger 23, which is a stacked heat exchanger, hasprimarily flat tubes 231, corrugated fins 232, and headers 233 a, 233 b,as shown in FIG. 3. FIG. 3 is an external perspective view of theoutdoor heat exchanger 23. The flat tubes 231, which are molded fromaluminum or an aluminum alloy, have flat surface parts 231 a that serveas heat transfer surfaces and a plurality of internal flow channels (notshown) through which refrigerant flows. The flat tubes 231 are arrayedin multiple levels so as to be superposed set apart by gaps (air passagespaces) with the flat surface parts 231 a being made to face up anddown. The corrugated fins 232 are fins made of aluminum or an aluminumalloy, bent into a corrugated formation. The corrugated fins 232 aredisposed in air passage spaces enclosed between vertically adjacent flattubes 231, and the troughs and peaks thereof are in contact with theflat surface parts 231 a of the flat tubes 231. The troughs, peaks, andflat surface parts 231 a are bonded by soldering or the like. Theheaders 233 a, 233 b are linked to the ends of the flat tubes 231arrayed in multiple levels in the vertical direction. The headers 233 a,233 b have the function of supporting the flat tubes 231, the functionof leading refrigerant into the internal flow channels of the flat tubes231, and the function of collecting refrigerant coming out of theinternal flow channels. When the outdoor heat exchanger 23 functions asa heat radiator of refrigerant, refrigerant flowing in through a firstinlet/outlet 234 of the first header 233 a is distributed mostly equallyto the internal flow channels of the topmost flat tube 231, and therefrigerant flows toward the second header 233 b, Having reached thesecond header 233 b, the refrigerant is distributed mostly equally tothe infernal flow channels of the second highest flat tube 231, and therefrigerant flows toward the first header 233 a. The refrigerant in theflat tubes 231 of odd-numbered levels flows toward the second header 233b, and the refrigerant in the flat tubes 231 of even-numbered levelsflows toward the first header 233 a. The refrigerant in the bottommostand even-numbered level flat tubes 231 flows toward the first header 233a, collects in the first header 233 a, and flows out through a secondinlet/outlet 235 of the first header 233 a. When the outdoor heatexchanger 23 functions as an evaporator of refrigerant, refrigerantflows in through the second inlet/outlet 235 of the first header 233 a,and after flowing through the flat tubes 231 and the headers 233 a, 233b in the opposite direction of when the outdoor heat exchanger functionsas a heat radiator of refrigerant, the refrigerant flows out through thefirst inlet/outlet 234 of the first header 233 a. When the outdoor heatexchanger 23 functions as a heat radiator of refrigerant, therefrigerant flowing in the flat tubes 231 radiates heat to the air flowpassing through the air passage spaces via the corrugated fins 232. Whenthe outdoor heat exchanger 23 functions as an evaporator of refrigerant,the refrigerant flowing in the flat tubes 231 absorbs heat from the airflow passing through the air passage spaces via the corrugated fins 232.Due to a stacked heat exchanger such as the one described above beingused as the outdoor heat exchanger 23, the capacity of the outdoor heatexchanger 23 is less than the capacity of the indoor heat exchanger 41.This point is described using FIG. 4, giving a package air-conditioneras an example. FIG. 4 is a graph showing the outdoor heat exchangercapacity/indoor heat exchanger capacity ratio according to capability.In FIG. 4, the symbol ⋄ represents a normal type (a cross-fin typeoutdoor heat exchanger) of a package air-conditioner, the symbol ♦represents a small diameter type of outdoor heat exchanger (a stackedoutdoor heat exchanger) of a package air-conditioner, the symbol Δrepresents a normal type (a cross-fin type outdoor heat exchanger) of aroom air-conditioner, and the symbol ▴ represents a small diameter typeof outdoor heat exchanger (a stacked outdoor heat exchanger) of a roomair-conditioner. According to FIG. 4, the outdoor heat exchangercapacity/indoor heat exchanger capacity ratio is less than 1.0 when onlythe outdoor heat exchanger is changed to a stacked heat exchanger havinga similar heat exchange performance, in contrast to when the outdoorheat exchanger and the indoor heat exchanger are both cross-fin typeheat exchangers. This means that not only is the capacity of a stackedheat exchanger less than the capacity of a cross-fin type outdoor heatexchanger, but it is also less than the capacity of a cross-fin typeindoor heat exchanger 41 connected thereto. Therefore, in theair-conditioning apparatus 1, excess refrigerant is produced during theair-cooling operation. In view of this, in the air-conditioningapparatus 1, the excess refrigerant is accommodated in the refrigerantstorage tank 25. According to FIG. 4, the refrigerant storage tank 25for accommodating excess refrigerant is preferably used when the outdoorheat exchanger capacity/indoor heat exchanger capacity ratio is 0.3 to0.9, but stable refrigerant control is made possible by using therefrigerant storage tank 25 also when the outdoor heat exchangercapacity/indoor heat exchanger capacity ratio is 1.0.

During the air-cooling operation, the first expansion mechanism 24functions as an upstream-side expansion mechanism for depressurizing therefrigerant that has radiated heat in the outdoor heat exchanger 23 toan intermediate pressure in the refrigeration cycle, and during theair-warming operation, the first expansion mechanism 24 functions as adownstream-side expansion mechanism for depressurizing the refrigeranttemporarily stored in the refrigerant storage tank 25 to a low pressurein the refrigeration cycle after the refrigerant has been depressurizedin the second expansion mechanism 26 as an upstream-side expansionmechanism. The first expansion mechanism 24 is provided to a portionnear the outdoor heat exchanger 23 in the liquid refrigerant tube 35. Anelectric expansion valve is used herein as the first expansion mechanism24.

During the air-cooling operation, the second expansion mechanism 26functions as a downstream-side expansion mechanism for depressurizingthe refrigerant temporarily stored in the refrigerant storage tank 25 toa low pressure in the refrigeration cycle, after the refrigerant hasbeen depressurized in the first expansion mechanism 24 as anupstream-side expansion mechanism. During the air-warming operation, thesecond expansion mechanism 26 functions as an upstream-side expansionmechanism for depressurizing the refrigerant that has radiated heat inthe indoor heat exchanger 41 to an intermediate pressure in therefrigeration cycle. The second expansion mechanism 26 is provided to aportion of the liquid refrigerant tube 35 that is near the liquid-sideshutoff valve 27. An electric expansion valve is used herein as thesecond expansion mechanism 26.

The refrigerant storage tank 25, which is provided between the firstexpansion mechanism 24 and the second expansion mechanism 26, is acontainer that can collect refrigerant as excess refrigerant, after therefrigerant has been depressurized by the first expansion mechanism 24or second expansion mechanism 26 functioning as an upstream-sideexpansion mechanism. For example, in a case in which the liquidrefrigerant quantity that can be accommodated in the indoor heatexchanger 41 is 1100 cc during the air-warming operation in which theindoor heat exchanger 41 functions as a heat radiator of refrigerant,and the liquid refrigerant quantity that can be accommodated in theoutdoor heat exchanger 23 is 800 cc during the air-cooling operation inwhich the outdoor heat exchanger 23 functions as a heat radiator ofrefrigerant, 300 cc of leftover liquid refrigerant that could not beaccommodated in the outdoor heat exchanger 23 during the air-coolingoperation is temporarily accommodated in the refrigerant storage tank25. The refrigerant just before entering the refrigerant storage tank25, for example, also includes a gas component produced when therefrigerant is depressurized in the first expansion mechanism 24 orsecond expansion mechanism 26 functioning as an upstream-side expansionmechanism. Therefore, the refrigerant is separated into a liquidcomponent and a gas component after entering the refrigerant storagetank 25, the liquid refrigerant is stored in the downstream side, andthe gas component is stored in the upstream side. The gas refrigerantseparated in the refrigerant storage tank 25 passes through a bypasstube 30 and flows to the intake tube 31 of the compressor 21. The liquidrefrigerant separated in the refrigerant storage tank 25 flows to theoutdoor heat exchanger 23 after being depressurized in the secondexpansion mechanism 26 or first expansion mechanism 24 functioning as anupstream-side expansion mechanism. The bypass tube 30 is provided so asto connect the top part of the refrigerant storage tank 25 and themiddle portion of the intake tube 31. A flow rate adjustment mechanism30 a is provided in the middle of the bypass tube 30. An electricexpansion valve is used herein as the flow rate adjustment mechanism 30a. The outlet of the bypass tube 30 may also be connected directly tothe compressor 21, rather than being connected to the middle portion ofthe intake tube 31.

The liquid-side shutoff valve 27 and the gas-side shutoff valve 28 arevalves provided to ports connecting with external devices and tubing(specifically, the liquid refrigerant communication tube 5 and the gasrefrigerant communication tube 6). The second expansion mechanism 26 isprovided to an end of the liquid refrigerant tube 35. The liquid-sideshutoff valve 27 is provided to an end of the second gas refrigeranttube 34.

The outdoor unit 2 has an outdoor fan 36 for drawing outdoor air intothe outdoor unit 2 and expelling the air to the exterior after the airhas undergone heat exchange with the refrigerant in the outdoor heatexchanger 23. The outdoor fan 36 herein is a propeller fan or the likedriven by an outdoor fan motor 37.

The outdoor unit 2 has an outdoor-side control part 38 for controllingthe actions of the components constituting the outdoor unit 2. Theoutdoor-side control part 38, which has a microcomputer, a memory, andthe like for performing control on the outdoor unit 2, is designed to becapable of exchanging control signals and the like with an indoor-sidecontrol part 44 of the indoor unit 4 via the transmission line 8 a.Specifically, a control part 8 for performing the operation controls forthe entire air-conditioning apparatus 1 is configured by the indoor-sidecontrol part 44, the outdoor-side control part 38, and the transmissionline 8 a which connects the control parts 38, 44.

The control part 8 is designed to be capable of controlling the actionsof the various devices and valves 21 a, 22, 24, 26, 30 a, 37, 43, etc.,on the basis of various operation settings, the values detected byvarious sensors, and the like.

<Refrigerant Communication Tubes>

The refrigerant communication tubes 5, 6, which are refrigerant tubesmachined on-site when the air-conditioning apparatus 1 is installed inan installation location such as a building, have various lengths and/ortube diameters according to the installation location and/orinstallation conditions such as the combination of the outdoor unit andthe indoor unit.

As described above, the refrigerant circuit 10 of the air-conditioningapparatus 1 is configured from the connection between the outdoor unit2, the indoor unit 4, and the refrigerant communication tubes 5, 6.During the air-cooling operation as a cooling operation, the refrigerantcircuit 10 is designed to perform a refrigeration cycle in whichrefrigerant flows sequentially through the compressor 21, the outdoorheat exchanger 23, the first expansion mechanism 24 as an upstream-sideexpansion mechanism, the refrigerant storage tank 25, the secondexpansion mechanism 26 as a downstream-side expansion mechanism, and theindoor heat exchanger 41. During the air-warming operation as a heatingoperation, the refrigerant circuit 10 is designed to perform arefrigeration cycle in which refrigerant flows sequentially through thecompressor 21, the indoor heat exchanger 41, the second expansionmechanism 26 as an upstream-side expansion mechanism, the refrigerantstorage tank 25, the first expansion mechanism 24 as a downstream-sideexpansion mechanism, and the outdoor heat exchanger 23. Theair-conditioning apparatus 1 is designed to be capable of performingvarious operations such as the air-cooling operation and the air-warmingoperation, by means of the control part 8 configured from theindoor-side control part 44 and the outdoor-side control part 38.

(2) Actions of Air Conditioning Apparatus

The air-conditioning apparatus 1 can perform an air-cooling operationand an air-warming operation as described above. The actions of theair-conditioning apparatus 1 during the air-cooling operation and theair-warming operation are described below.

<Air-Warming Operation>

During the air-warming operation, a switch is performed in which theswitching mechanism 22 is in the state shown by the dashed lines in FIG.1, i.e., the second port 22 b and the fourth port 22 d are communicated,and the first port 22 a and the third port 22 c are communicated.

In this refrigerant circuit 10, low-pressure refrigerant in therefrigeration cycle is drawn into the compressor 21 and discharged afterbeing compressed to a high pressure.

The high-pressure refrigerant discharged from the compressor 21 is sentthrough the switching mechanism 22, the gas-side shutoff valve 28, andthe gas refrigerant communication tube 6 to the indoor heat exchanger41.

The high-pressure refrigerant sent to the indoor heat exchanger 41undergoes heat exchange with indoor air and radiates heat in the indoorheat exchanger 41. The indoor air is thereby heated. Because thecapacity of the indoor heat exchanger 41 is greater than the capacity ofthe outdoor heat exchanger 23, most of the liquid refrigerant isaccommodated in the indoor heat exchanger 41 during the air-warmingoperation.

The high-pressure refrigerant that has radiated heat in the indoor heatexchanger 41 is sent through the liquid refrigerant communication tube 5and the liquid-side shutoff valve 27 to the second expansion mechanism26 functioning as an upstream-side expansion mechanism.

The refrigerant sent to the second expansion mechanism 26 isdepressurized to an intermediate pressure by the second expansionmechanism 26, and is then sent to the refrigerant storage tank 25. Therefrigerant just before entering the refrigerant storage tank 25includes a gas component produced when the refrigerant is depressurizedin the second expansion mechanism 26, but after entering the refrigerantstorage tank 25, the refrigerant is divided into a liquid component anda gas component, the liquid refrigerant is stored in the lower side, andthe gas refrigerant is stored in the upper side. At this time, becausethe flow rate adjustment mechanism 30 a of the bypass tube 30 iscontrolled to an open state, the gas refrigerant in the refrigerantstorage tank 25 passes through the bypass tube 30 and heads to theintake tube 31 of the compressor 21. The liquid refrigerant in therefrigerant storage tank 25 is sent to the outdoor heat exchanger 23after being depressurized to a low pressure by the first expansionmechanism 24 functioning as a downstream-side expansion mechanism.

The low-pressure refrigerant sent to the outdoor heat exchanger 23undergoes heat exchange with outdoor air supplied by the outdoor fan 36and evaporates in the outdoor heat exchanger 23. At this time, therefrigerant flowing into the outdoor heat exchanger 23 is reduced by thegas-liquid separating process in the refrigerant storage tank 25, aswell as the process of drawing the gas-liquid separated gas refrigerantthrough the bypass tube 30 into the compressor 21. Therefore, the flowrate of refrigerant flowing through the outdoor heat exchanger 23decreases, pressure loss can be reduced proportionately, and thedepressurization loss in the refrigeration cycle can therefore bereduced.

The low-pressure refrigerant evaporated in the outdoor heat exchanger 23is drawn through the switching mechanism 22 back into the compressor 21.

<Air-Cooling Operation>

During the air-cooling operation, a switch is performed in which theswitching mechanism 22 is in the state shown by the solid lines in FIG.1, i.e., the second port 22 b and the third port 22 c are communicated,and the first port 22 a and the fourth port 22 d are communicated.

In this refrigerant circuit 10, low-pressure refrigerant in therefrigeration cycle is drawn into the compressor 21 and discharged afterbeing compressed to a high pressure.

The high-pressure refrigerant discharged from the compressor 21 is sentthrough the switching mechanism 22 to the outdoor heat exchanger 23.

The high-pressure refrigerant sent to the outdoor heat exchanger 23undergoes heat exchange with outdoor air and radiates heat in theoutdoor heat exchanger 23.

The high-pressure refrigerant that has radiated heat in the outdoor heatexchanger 23 is sent to the first expansion mechanism 24 functioning asan upstream-side expansion mechanism, depressurized to an intermediatepressure by the first expansion mechanism 24, and then sent to therefrigerant storage tank 25. Because the capacity of the outdoor heatexchanger 23 is equal to or less than the capacity of the indoor heatexchanger 41 here, the outdoor heat exchanger 23 is not able toaccommodate all of the liquid refrigerant during the air-coolingoperation. Therefore, the liquid refrigerant that could not beaccommodated in the outdoor heat exchanger 23 is accumulated in therefrigerant storage tank 25, and the refrigerant storage tank 25 isfilled with liquid refrigerant. The refrigerant just before entering therefrigerant storage tank 25 includes a gas component produced when therefrigerant is depressurized in the first expansion mechanism 24, butafter entering the refrigerant storage tank 25, the refrigerant isdivided into a liquid component and a gas component, the liquidrefrigerant is stored in the lower side, and the gas refrigerant isstored in the upper side. At this time, because the flow rate adjustmentmechanism 30 a of the bypass tube 30 is controlled to an open state, thegas refrigerant in the refrigerant storage tank 25 passes through thebypass tube 30 and heads to the intake tube 31 of the compressor 21. Theliquid refrigerant in the refrigerant storage tank 25 is sent throughthe liquid-side shutoff valve 27 and the liquid refrigerantcommunication tube 5 to the indoor heat exchanger 41 after beingdepressurized to a low pressure by the second expansion mechanism 26functioning as a downstream-side expansion mechanism.

The low-pressure refrigerant sent to the indoor heat exchanger 41undergoes heat exchange with indoor air and evaporates in the indoorheat exchanger 41. The indoor air is thereby cooled. At this time, therefrigerant flowing into the indoor heat exchanger 41 is reduced by thegas-liquid separating process in the refrigerant storage tank 25, aswell as the process of drawing the gas-liquid separated gas refrigerantthrough the bypass tube 30 into the compressor 21. Therefore, the flowrate of refrigerant flowing through the indoor heat exchanger 41decreases, pressure loss can be reduced proportionately, and thedepressurization loss in the refrigeration cycle can therefore bereduced.

The low-pressure refrigerant evaporated in the indoor heat exchanger 41is drawn through the gas refrigerant communication tube 6, the gas-sideshutoff valve 28, and the switching mechanism 22 back into thecompressor 21.

(3) Characteristics of Air-Conditioning Apparatus

The air-conditioning apparatus 1 of the present embodiment has thefollowing characteristics.

<A>

In the air-conditioning apparatus 1, as described above, the indoor heatexchanger 41 is a cross-fin type heat exchanger, the outdoor heatexchanger 23 is a stacked heat exchanger, and the capacity of theoutdoor heat exchanger 23 is 100% or less of the capacity of the indoorheat exchanger 41.

Therefore, in the air-conditioning apparatus 1, excess refrigerant isproduced during the air-cooling operation as a cooling operation. Whentoo much of this excess refrigerant spreads from the indoor heatexchanger 41 having a gas-phase portion to portions as far as the intakeside of the compressor 21, there is a risk that refrigerant control willbe hindered.

In view of this, in the air-conditioning apparatus 1, the refrigerantstorage tank 25 for storing refrigerant depressurized by anupstream-side expansion mechanism is provided between one of the firstexpansion mechanism 24 and the second expansion mechanism 26 as anupstream-side expansion mechanism, and the other of the first expansionmechanism 24 and the second expansion mechanism 26 as a downstream-sideexpansion mechanism, as described above. In the air-conditioningapparatus 1, the excess refrigerant that can no longer be accommodatedin the outdoor heat exchanger 23 during the air-cooling operation isthen accommodated in the refrigerant storage tank 25 positioned in thevicinity of the downstream side of the outdoor heat exchanger 23.

It is thereby possible to prevent hindrances to refrigerant control inthe air-conditioning apparatus 1 because it is possible to prevent toomuch refrigerant from spreading from the indoor heat exchanger 41 havinga gas-phase portion to portions as far as the intake side of thecompressor 21.

<B>

In the air-conditioning apparatus 1, a bypass tube 30 is provided asdescribed above. The bypass tube 30 is designed to lead the gascomponent of the refrigerant accumulated in the refrigerant storage tank25 to either the compressor 21 or the intake tube 31 of the compressor21.

In the air-conditioning apparatus 1, refrigerant depressurized in one ofthe first expansion mechanism 24 and the second expansion mechanism 26as an upstream-side expansion mechanism is separated info a liquidcomponent and a gas component in the refrigerant storage tank 25, andthe gas component heads toward the bypass tube 30.

The gas component, which does not contribute to evaporation, therebyceases to flow into the outdoor heat exchanger 23 functioning as anevaporator of refrigerant during the air-warming operation in theair-conditioning apparatus 1, it is therefore possible toproportionately reduce the flow rate of refrigerant flowing through theoutdoor heat exchanger 23 functioning as an evaporator of refrigerant,and the depressurization loss in the refrigeration cycle can be reduced.

<C>

When the operating frequency of the compressor 21 is high, there is arisk that gas-liquid two-phase refrigerant from the refrigerant storagetank 25 will pass through the bypass tube 30, return to the compressor21 or the intake tube 31 of the compressor 21, and be drawn into thecompressor 21.

However, in the air-conditioning apparatus 1, because the flow rateadjustment mechanism 30 a is provided to the bypass tube 30, the liquidcomponent of the gas-liquid two-phase refrigerant is depressurized andevaporated.

It is thereby possible in the air-conditioning apparatus 1 to preventthe liquid component from returning to the compressor 21 or the intaketube 31 of the compressor 21.

<D>

During the air-warming operation in the air-conditioning apparatus 1,refrigerant that has passed through the flow rate adjustment mechanism30 a converges with refrigerant which has evaporated in the indoor heatexchanger 41 and/or the outdoor heat exchanger 23, and then heads to thecompressor 21 or the intake tube 31 of the compressor 21. At this time,in the case that the flow rate adjustment mechanism 30 a is an electricexpansion valve, the state of the refrigerant just before being drawninto the compressor 21 can be adjusted more optimally by controlling thevalve opening degree. Moreover, because the flow rate of refrigerantreturning to the compressor 21 can be increased or reduced bycontrolling the valve opening degree of the flow rate adjustmentmechanism 30 a, the refrigerant circulation flow rate, i.e. the flowrate of refrigerant flowing through the indoor heat exchanger 41 can becontrolled according to the refrigeration load on the indoor heatexchanger 41 side.

(4) Modification 1

In the above embodiment, a container for storing refrigerant is employedas the refrigerant storage tank 25, but refrigerant storage is notlimited as such, and a cyclone-type gas-liquid separator such as the oneshown in FIG. 5 may be employed, for example.

The refrigerant storage tank 25 of the present modification hasprimarily a cylindrical container 251, a first connecting tube 252, asecond connecting tube 253, and a third connecting tube 254.

The first connecting tube 252 is linked in the tangential direction ofthe circumferential side wall of the cylindrical container 251,communicating the interior of the cylindrical container 251 and thesecond expansion mechanism 26 or first expansion mechanism 24 as adownstream-side expansion mechanism. The second connecting tube 253 islinked to the bottom wall of the cylindrical container 251,communicating the interior of the cylindrical container 251 and thefirst expansion mechanism 24 or second expansion mechanism 26 as anupstream-side expansion mechanism. The third connecting tube 254 islinked to the top wall of the cylindrical container 251, communicatingthe interior of the cylindrical container 251 and the bypass tube 30.

Due to this configuration, intermediate-pressure refrigerant flowinginto the cylindrical container 251 through the first connecting tube 252flows so as to eddy along the internal peripheral surface 251 a of thecircumferential side wall of the cylindrical container 251, at whichtime the liquid refrigerant adheres to the internal peripheral surface251 a, and the liquid refrigerant and gas refrigerant are efficientlyseparated.

The liquid refrigerant falls due to gravity, accumulates in the lowerside, and flows out of the cylindrical container 251 through the secondconnecting tube 253. The gas refrigerant rises while swirling,accumulates in the upper side, and flows out of the cylindricalcontainer 251 through the third connecting tube 254.

In the present modification, gas-liquid separation can be efficientlyperformed because a cyclone-type gas-liquid separator is employed as therefrigerant storage tank 25 as described above. The refrigerant storagetank 25 composed of a gas-liquid separator has both a refrigerantstorage function of accumulating liquid refrigerant and a function ofseparating the liquid component and gas component, thereby contributingto simplifying the apparatus configuration because there is no need toprovide both a refrigerant storage container and a gas-liquid separator.

(5) Modification 2

In the above embodiment and Modification 1, an example was given inwhich the outdoor heat exchanger 23 is a stacked heat exchanger having aplurality of flat tubes 231 and corrugated fins 232. In this outdoorheat exchanger 23, the plurality of flat, tubes 231 are arrayed so as tobe superposed set apart by gaps, and the corrugated fins 232 areenclosed between adjacent flat tubes 231.

However, the outdoor heat exchanger 23 is not limited to theconfigurations in the above embodiment and Modification 1, and may be astacked heat exchanger having a plurality of flat tubes 231 arrayed soas to be superposed set apart by gaps, and fins 236 in which notches 236a are formed, the flat tubes 231 being inserted into the notches, asshown in FIGS. 6 and 7, for example.

The same operational effects as those of the above embodiment andModification 1 can be achieved in this case as well.

(6) Modification 3

In the above embodiment and Modification 1, an example was given inwhich the outdoor heat exchanger 23 is a stacked heat exchanger having aplurality of flat tubes 231 and corrugated fins 232. In this outdoorheat exchanger 23, the plurality of flat tubes 231 are arrayed so as tobe superposed set apart by gaps, and the corrugated fins 232 areenclosed between adjacent flat tubes 231.

However, the outdoor heat exchanger 23 is not limited to theconfigurations in the above embodiment and Modification 1, and may havea configuration in which the flat tubes are molded into serpentineshapes and the fins are enclosed between the mutually adjacent surfacesof the flat tubes, for example.

The same operational effects as those of the above embodiment andModifications 1 and 2 can be achieved in this case as well.

(7) Modification 4

In the above embodiment and Modifications 1 to 3, the outdoor heatexchanger 23 is a stacked heat exchanger having a plurality of flattubes 231, corrugated fins 232, and/or fins 236 in which notches 236 aare formed. In the case of a refrigeration apparatus in which theoutdoor heat exchanger 23 is cooled by water during the air-coolingoperation, for example, the outdoor heat exchanger 23 and the indoorheat exchanger 41 may both be cross-fin type heat exchangers, configuredsuch that the diameter of the heat transfer tubes in the outdoor heatexchanger 23 is less than the diameter of the heat transfer tubes in theindoor heat exchanger 41.

The same operational effects as those of the above embodiment andModifications 1 to 3 can be achieved in this case as well.

(8) Modification 5

In the above embodiment and Modifications 1 to 4, various refrigerantscan be used as the refrigerant sealed within the refrigerant circuit 10,but R32, a type of HFC-based refrigerant, could be used as one typethereof, for example.

However, when R32 is used as the refrigerant in the refrigerationapparatus, refrigerator oil sealed with the refrigerant in order tolubricate the compressor 21 tends to have extremely low solubility inlow-temperature conditions. Therefore, at a low pressure in therefrigeration cycle, the solubility of the refrigerator oil greatlydecreases due to the decrease in refrigerant temperature. During theair-cooling operation in the refrigerant circuit 10, there is lowpressure in the refrigeration cycle in the circuit portion beginningafter passing through the second expansion mechanism 26 functioning as adownstream-side expansion mechanism and leading through the indoor heatexchanger 41 up to intake in the compressor 21. During the air-warmingoperation, there is low pressure in the refrigeration cycle in thecircuit portion beginning after passing through the first expansionmechanism 24 functioning as a downstream-side expansion mechanism andleading through the outdoor heat exchanger 23 up to intake in thecompressor 21. The refrigerator oil when R32 is used as the refrigerantcould be ether-based synthetic oil having any compatibility with R32,mineral oil or alkyl benzene-based synthetic oil having no compatibilitywith R32, or the like. With ether-based synthetic oil, compatibility islost when the temperature decreases to about −5° C., and with mineraloil or alkyl benzene-based synthetic oil, there is no compatibility atconditions of higher temperature than ether-based synthetic oil. WhenR32 is used as the refrigerant in a conventional refrigeration apparatushaving a refrigerant storage tank on the intake side of the compressor,for example, the refrigerant and the refrigerator oil separate into twolayers in the refrigerant storage tank which has a low pressure in therefrigeration cycle, and the refrigerator oil has difficulty returningto the compressor.

However, in the refrigeration apparatus 1 of the present modification,because a refrigerant storage tank 25 is provided between the first andsecond expansion mechanisms 24, 26 as an upstream-side expansionmechanism and a downstream-side expansion mechanism as indicated in theabove embodiment and Modifications 1 to 4, two-layer separation is lesslikely to occur in the intake side of the compressor 21 and refrigeratoroil returns more readily to the compressor 21, in comparison to cases inwhich the refrigerant storage tank is provided to the intake side of thecompressor 21.

Thus, in the refrigeration apparatus 1 of the present modification, dueto the refrigerant storage tank 25 being provided between the first andsecond expansion mechanisms 24, 26 as an upstream-side expansionmechanism and a downstream-side expansion mechanism, if is possible toresolve not only the problem of excess refrigerant produced by thecapacity of the outdoor heat exchanger 23 being equal to or less thanthe capacity of the indoor heat exchanger 41, due to factors such as astacked heat exchanger being used as the outdoor heat exchanger 23, butalso the problem of oil returning to the compressor 21, caused by usingR32 as the refrigerant.

INDUSTRIAL APPLICABILITY

The present invention is widely applicable in refrigeration apparatusesthat can perform a cooling operation and a heating operation.

REFERENCE SIGNS LIST

-   1 Air-conditioning apparatus (refrigeration apparatus)-   21 Compressor-   23 Outdoor heat exchanger-   24, 26 Expansion mechanisms-   25 Refrigerant storage tank-   30 Bypass tube-   30 a Flow rate adjustment mechanism-   41 Indoor heat exchanger

CITATION LIST Patent Literature

<Patent Literature 1>

Japanese Laid-open Patent Application No. 6-143991

1. A refrigeration apparatus in which a refrigerant flows sequentiallythrough a compressor, an outdoor heat exchanger, expansion mechanisms,and an indoor heat exchanger during a cooling operation, and therefrigerant flows sequentially through the compressor, the indoor heatexchanger, the expansion mechanisms, and the outdoor heat exchangerduring a heating operation; the indoor heat exchanger being a cross-finheat exchanger and the outdoor heat exchanger being a stacked heatexchanger, and a capacity ratio of the outdoor heat, exchanger to theindoor heat exchanger is 0.3 to 0.9; the expansion mechanisms includingan upstream-side expansion mechanism configured to depressurize therefrigerant from a high pressure in a refrigerant cycle to anintermediate pressure in the refrigerant cycle and a downstream-sideexpansion mechanism configured to depressurize the refrigerant that hasbeen depressurized in the upstream-side expansion mechanism from theintermediate pressure in the refrigerant cycle to a low pressure in therefrigerant cycle; the outdoor heat exchanger, the upstream-sideexpansion mechanism and the downstream-side expansion mechanism beingprovided in an outdoor unit, the indoor heat exchanger being provided inan indoor unit, and the outdoor unit and the indoor unit being connectedvia a liquid refrigerant communication tube; the refrigerant being R32;a refrigerant storage tank configured and arranged to store therefrigerant depressurized to the intermediate pressure in therefrigerant cycle by the upstream-side expansion mechanism beingprovided between the upstream-side expansion mechanism and thedownstream -side expansion mechanism; and the refrigerant storage tankstoring an excess refrigerant produced during the cooling operation dueto a capacity of the outdoor heat exchanger being less than a capacityof the indoor heat exchanger.
 2. A refrigeration apparatus in which arefrigerant flows sequentially through a compressor, an outdoor heatexchanger, expansion mechanisms, and an indoor heat exchanger during acooling operation, and the refrigerant flows sequentially through thecompressor, the indoor heat exchanger, the expansion mechanisms, and theoutdoor heat exchanger during a heating operation; a capacity of theoutdoor heat exchanger being 30% to 90% of a capacity of the indoor heatexchanger; the expansion mechanisms including an upstream-side expansionmechanism, configured to depressurize the refrigerant from a highpressure in a refrigerant cycle to an intermediate pressure in therefrigerant cycle and a downstream-side expansion mechanism configuredto depressurize the refrigerant that has been depressurized in theupstream-side expansion mechanism from the intermediate pressure in therefrigerant cycle to a low pressure in the refrigerant cycle; theoutdoor heat exchanger, the upstream-side expansion mechanism and thedownstream-side expansion mechanism being provided in an outdoor unit,the indoor heat exchanger being provided in an indoor unit, and theoutdoor unit and the indoor unit being connected via a liquidrefrigerant communication tube; the refrigerant being R32; a refrigerantstorage tank configured and arranged to store the refrigerantdepressurized to the intermediate pressure in the refrigerant cycle bythe upstream-side expansion mechanism being provided between theupstream-side expansion mechanism and the downstream-side expansionmechanism; and the refrigerant storage tank boring an excess refrigerantproduced during the cooling operation due to a capacity of the outdoorheat exchanger being less than a capacity of the indoor heat exchanger.3. The refrigeration apparatus according to claim 2, wherein the outdoorheat exchanger is a stacked heal exchanger having a plurality of flatlubes arrayed so as to be superposed set apart by gaps, and finssandwiched between adjacent flat tubes.
 4. The refrigeration apparatusaccording to claim 2, wherein the outdoor heat exchanger is a stackedheat exchanger having a plurality of flat tubes arrayed so as to besuperposed set apart by gaps, and fins having notches formed thereinwhere the flat tubes are inserted.
 5. The refrigeration apparatusaccording to claim 2, wherein the outdoor heat exchanger is a stackedheat exchanger having flat tubes molded into serpentine shapes, and finsinserted between mutually adjacent surfaces of the flat tubes.
 6. Therefrigeration apparatus according to claim 2, wherein the outdoor heatexchanger and the indoor heat exchanger are cross-fin heat exchangers;and a diameter of heat transfer tubes in the outdoor heat exchanger isless than a diameter of heat transfer tubes in the indoor heatexchanger.
 7. The refrigeration apparatus according to claim 2, furthercomprising a bypass tube configured and arranged to lead a gas componentof the refrigerant accumulated in the refrigerant storage tank to thecompressor or to a refrigerant tube on an intake side of the compressor.8. The refrigeration apparatus according to claim 7, wherein the bypasstube has a flow rate adjustment mechanism.
 9. The refrigerationapparatus according to claim 2, wherein the refrigerant storage tank isa gas-liquid separator.
 10. The refrigeration apparatus according toclaim 1, wherein the outdoor heat exchanger is a stacked heat exchangerhaving a plurality of flat tubes arrayed so as to be superposed setapart by gaps, and fins sandwiched between adjacent flat tubes.
 11. Therefrigeration apparatus according to claim 1, wherein the outdoor heatexchanger is a slacked heat exchanger having a plurality of flat tubesarrayed so as to be superposed set apart by gaps, and fins havingnotches formed therein where the flat tubes are inserted.
 12. Therefrigeration apparatus according to claim 1, wherein the outdoor heatexchanger is a stacked heat exchanger having flat tubes molded intoserpentine shapes, and fins inserted between mutually adjacent surfacesof the flat tubes.
 13. The refrigeration apparatus according to claim 1,further comprising a bypass tube configured and arranged to lead a gascomponent of the refrigerant accumulated in the refrigerant storage tankto the compressor or to a refrigerant tube on an intake side of thecompressor.
 14. The refrigeration apparatus according to claim 13,wherein the bypass tube has a flow rate adjustment mechanism.
 15. Therefrigeration apparatus according to claim 1, wherein the refrigerantstorage tank is a gas-liquid separator.